LISA satellite and lasers
Posted on 04/19/2005 5:20:02 PM PDT by PatrickHenry
A hundred years ago, Albert Einstein published his theory of relativity. On this occasion, Euronews' Space magazine plunges into the subject of gravitational waves and features the joint ESA-NASA "LISA" mission which hopes to detect them in space.
The existence of gravitational waves stems from Einstein's postulates. When very massive bodies are disturbed, they radiate waves or ripples that travel through space. When these waves hit an object, this will make minute movements as a consequence of the deformation of the space-time texture in which it is at rest.
The Laser Interferometer Space Antenna (LISA) mission, whose launch is envisaged for 2013, will use laser interferometers - very sensitive tools to measure tiny variations in the distance between objects – and proof masses on board three spacecraft flying in formation.
The system is designed to detect low-frequency gravitational waves which originate from, for instance, black holes swallowing massive neutron stars or binary star systems revolving around each other. They were also produced at the very origins of time, when the Big Bang occurred.
"As far as we know, the Universe began 13.7 billion years ago," explains Karsten Danzmann, Principal Investigator for the LISA mission at the Max-Planck-Institut fur Gravitationsphysik in Hanover in Germany.
"We have the dream of listening to that Big Bang itself by detecting and studying gravitational waves. It will give us a chance of listening to the dark, invisible side of the Universe."
Gravitational waves are so weak they are extremely difficult to hear. Because of our planet's own gravity, laser interferometers on Earth can only detect high frequencies, stemming from sources which are relatively close.
"If you want to listen to the high pitch notes of a concert you can do so with small ears, but if you want to listen to the real low pitches, you need big ears, and the only place where you can have big ears is in space," says Danzmann.
The LISA mission is one of the most ambitious ever undertaken: positioning and flying three spacecraft in a triangular formation, 5 million kilometres apart. The constellation will orbit the Sun, following the Earth at a distance of 50 million kilometres so as not to be perturbed by its gravity.
Infrared lasers will be beamed between the spacecraft, arriving on small 2-kilogram proof masses, 4-centimetre cubes made of gold and platinum.
At the University of Trent in Italy, Euronews was able to see the first of these proof masses destined for the LISA Pathfinder precursor mission. Due to be launched in 2008, its single satellite will test the general concepts and technologies of the LISA mission.
"We will be flying totally new technologies in space," says Professor Stefano Vitale, the Principal Investigator for the LISA Pathfinder mission. "The structure of the satellites will protect the proof masses. They will float much like astronauts hover in the void of space. But their precise position will be constantly monitored to detect when they are influenced by a passing gravity wave."
Precise is a euphemism when one details the accuracy of such measurements: LISA will need to detect infinitely minute movements of the proof masses, of the order of a tenth of an atom, that is a billionth of a millimetre! It will also identify the polarisation of waves, and thus the direction they come from.
The detection of these gravitational waves will complete the missing links in Einstein's theory of relativity and throw wide-open a new avenue of exploration in fundamental physics and astronomy.
"Einstein had foreseen the eventual detection of gravitational waves," concludes Stefano Vitale. "But a hundred years ago, no suitable instruments were available and Einstein's work was entirely theoretical. Now we have the technologies, we are picking up the challenge, and he would no doubt be greatly pleased to see that we are pursuing his work."
[A bit more text and pics are at the original article.]
"It depends. Are gravity waves longitudinal or transversal? In other words, are they like sound waves where the oscillation parallels the direction of propagation, or are they like light waves where the electric field oscillates perpendicular to the direction of propagation?"
Great question. Sound is longitudinal because the medium is compressed by the energy from the sound source. Light is transversal because the electric and magnetic fields collapse as they propogate the photon.
As a wild guess, I'd say transversal. There's no medium to compress. Gravity is supposed to have quanta like light as well, (although I suppose it's far smaller, since gravity is a far weaker force).
I'd say we'll have a better idea after this satellite records gravity waves--if it does.
"Detecting gravitational waves would be nice. It would be a way to confirm the speed with which gravity propogates, which is still an open question."
Gravity propogates at c. (the speed of light)
That has been known for a while now.
Bones
Thanks for the ping!
From what I understand, that is an assumption, not a fact. Its assumed because nothing is supposed to travel faster than light, but others assume gravity propogates instantaneously.
I really don't know much about gravity waves, but the article mentions detecting the polarization of them. Polarization only makes sense for transverse waves. There is no way a longitudinal wave can be polarized.
"100 quatloos on the newcomer!"
I will have to look up the specifics.. but an expirement was done some time ago, which had something to do with Jupiter occulting some star.. in which the observations indicated that gravity propgates at the speed of light.
It's been so long (years) since I read that article, I will have to try and search for the info again..
Again I could be wrong, because it's been a while... but that is how I remember it. Will post if I find it, you might be right.
Bones
We had at least one thread on that, right here on FreeRepublic. But it was about 2 or 3 years ago. Maybe more.
Ah.. I just skimmed the artcicles so far but will read them later.
So the experiment did say that but then there was debate over it.. interesting.. thanks for finding that, I had been wondering.
Bones
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